(1) Field of the Invention
This invention relates to the field of semiconductor electronic devices and more specifically to semiconductor integrated circuit devices in which an improved method for depositing protective layers of silicon oxynitride is used to provide increased manufacturability by improving yield and reliability for such devices.
(2) Description of the Prior Art
The manufacture of semiconductor integrated circuit devices is achieved by the use of a variety of thin films of materials which are deposited and shaped to perform each of the specialized functions required for the effective performance of such devices. A semiconductor substrate is used for the fabrication of electrical elements and components which are then interconnected electrically to form the desired circuit and function. Due to the need for constantly increased performance, the dimensions of the components and their separation have become smaller to minimize the separation and hence the time delay for propagation of electrical signals in the circuit. This has resulted not only in smaller device dimensions but also in reduced dimensions of all other aspects of device fabrication. Thus, the thicknesses of the thin films of conductive materials and the insulating and protective layers employed in the devices have decreased in proportion. The decreasing thicknesses of interconnection patterns of aluminum, as an example of a widely used conductive material, results in an increased susceptibility to corrosion by such substances as moisture, which can lead to an increase in electrical resistance or even open circuits. Likewise, the decreased thicknesses of protective layers of material deposited over components and elements such as aluminum may give rise to a diminished ability to afford a protective barrier against moisture.
Agents such as moisture or certain gaseous ambients can also give rise to changes in the surface electrical properties of the semiconductor substrate and its various elements. In addition to permitting greater degrees of permeation by chemical species, the reduced thickness of insulating and passivating films and layers also leads to a greater degree of transmission of electrically charged species such as energetic or "hot" electrons from one device region to another where such charge may be trapped, interfering with the electrical operation of the device. To minimize this phenomenon, thin insulating layers with superior dielectric properties are increasingly required.
For the reasons mentioned, thin films of barrier materials have been devised to act as blocking or hindering agents to deleterious species when deposited over the various elements of semiconductor integrated circuit devices. Originally, layers of silicon nitride, Si.sub.3 N.sub.4, were found to be superior to silicon oxide for reducing the transmission of deleterious species such as sodium and potassium ions, and the higher value of the relative dielectric constant was desirable for electrical purposes. More recently, an even more effective material for this purpose is the compound formed among the elements silicon, nitrogen, and oxygen which is generically referred to as silicon oxynitride and is written as SiO.sub.x N.sub.y where x and y refer to the variable amounts of oxygen and nitrogen respectively depending on the details of the method of deposition. This type of material in the form of a thin film can function to minimize the sensitivity of the semiconductor surface electrical potential to various ambients during the processes of device fabrication and later in operation. It also serves as a barrier to diffusion of moisture and such unwanted ionic species as sodium and potassium ions. As a very thin film, it is more effective in minimizing the passage and trapping of hot electrons.
Silicon oxynitride layers have been deposited from various combinations of gases such as silane SiH.sub.4, silane derivatives Rsi, or organosiloxanes ROSi to supply the silicon atoms and oxygen- and nitrogen-containing gases to supply these atomic species in the desired proportions in layers deposited by the process of chemical vapor deposition. A particularly useful gas is nitrous oxide N.sub.2 O which contains both. Other possibilities are combinations of gases such as ammonia NH.sub.3, oxygen O.sub.2, etc. The use of an electrical plasma sustained in the reacting gases to enhance the deposition rate or improve the properties of the deposited film or both has been discussed in the literature. For example, the use of the combination of tetraethoxysilane (TEOS)+N.sub.2 +NH.sub.3 plasma-enhanced CVD processes to produce films of silicon oxynitride is discussed by Harada in U.S. Pat. No. 5,362,686. The use of nitrous oxide is not discussed and the method of plasma generation and sustenance is not described in any detail. Other descriptions of the use of silicon oxynitride deposited layers for various purposes in electrical device fabrication by (U.S. Pat. No. 4,381,595) and (U.S. Pat. No. 5,071,790) mention electrical interconnections on a semiconductor substrate, but neither the use of nitrous oxide nor the details of the plasma process are discussed.